Turbine vane prediction and classification gage and gaging method

ABSTRACT

An instrument and method for prediction and classification gaging of production turbine vanes without distortion of the vanes. In its prediction-gaging mode, the instrument gages selected airfoil dimensions of a production turbine vane and master and provides a figure of merit readout representing the difference between the effective class values of the master and vane resulting from the difference, if any, in their corresponding airfoil dimensions. This figure of merit is converted to an angle at which the class surface of the vane must be machined to provide the vane with a selected class value. In its classification-gaging mode, the instrument gages the selected airfoil dimensions and the class face angle of the machined vane and provides a readout representing the actual class value of the machined vane. The airfoil dimensions and class surface are gaged with electrical transducer in such a way that there is no distortion of the master or vane.

United States Patent Inventors Appl. No. Filed Patented Assignee TURBINEVANE PREDICTION AND CLASSIFICATION GAGE AND GAGING METHOD 22 Claims, 20Drawing Figs.

Int. Cl

Field (DI-S68 I 1111: 5:11:32:111:2...1:

151.13,151.21,151.3,151.31,151.1,151.32; 73/22s-231; 29/i56.8; 33/168,173; 72 1 1, l6;

5' ever [56] References cnu UNITED STATES PATENTS 3,147,370 9/1964Lowman 235/151.13 3,226,967 1/1966 Paille etal. 29/156.8X

Primary Examiner-Eugene G. Botz Assistant Examiner-Jerry SmithAnomeys-Daniel T. Anderson, Donald R. Nyhagen and Jerry A. DinardoABSTRACT: An instrument and method for prediction and classificationgaging of production turbine vanes without distortion of the vanes. inits prediction-gaging mode, the instrument gages selected airfoildimensions ofa production turbine vane and master and provides a figureof merit readout representing the difference between the effectiveclam-1 values of the masterand vane resulting from the difierenee. ifany. in their corresponding airfoil dimensions. This figure of merit isconverted to an angle at which the class surface of the vane must bemachined to provide the vane with a selected class value. in itsclassification-gaging mode, the instrument gages the selected airfoildimensions and the class face angle of the machined vane and provides areadout representing the actual class value of the machined vane. Theairfoil dimensions and class surface are gaged with electricaltransducer in such a way that there is no distortion of the master orvane.

M Para 9 1 SUMMATiON manner:

lSAMDLE/NULDCIDCUIY STIOEE lAMPLEI 140w mic un PATENTED UECl 4 ll17lSHEET 1 BF 9 SURFACE Charles l Mueller Ronald L. Samuels Wallace IVl.Porter William Penninlglon Jr.

INVAENTURS B I dtwea /6 j ATTORNEY PATENTEU DEC] 4 Ian SHEET 2 BF 9Charles L. Muller Ronald L Somuels Wallace IV] Review WilliamPenningi'on Jr INVMN'lURS ATTORNEY PATENTEUUEEMIQYI 352K997 sum w UF 9ATTORNEY K I n 3 .i N MG V WM\ Fwu n L MD: I ln 8 a %d C m 2 F N m m mmM QRWW [u CLASS 273 SURFACE PATENTEUuEcmsn 3627897 SHEET 5 BF 9 I62 /|es2 Charles L. Mueller Ronald L. Samueis "4 no WqHuce IVI. Porter rW||||0m Pennington \Jx VITL INVIiN'lU/(S \X\] XQ I |82 '78 I76 |8Q yFig. I5 4 ATTORNEY PATENTEUDECMIQYI 3,627,897

SHEET 5 BF 9 Charles L. Mueller Ronald L. Samuels Wallace M. Porrer MWilliam Pennington Jr [NV/5N! ()R 5 I94 ZZW@/% M ATTORNEY 'lftllltlMNlEVANIE PlitlElDllCTllQN AND CLASSH HCATHON GAGE AND GAGllNG METHUDBACKGROUND OF THE INVENTION 1. Field of the invention This inventionrelates generally to turbines and more particularly to a turbine vaneprediction and classification-gaging instrument and method.

The invention has primary application to and will be described inconnection with gaging of vanes for jet aircraft engines. However, thepresent instrument may be utilized for gaging other types of turbinevanes and thus should not be regarded as limited in application to thegaging of jet engine turbine vanes.

2. Prior Art .let aircraft engines have a final stage nozzle ringcomposed of a set of stationary turbine vanes each having tip and rootbuttresses and an intervening airfoil section. These vanes are assembledside-by-side in an annular configuration. One edge surface of the tipbuttress of each vane serves as a reference surface and is termed aclass surface. Each pair of adjacent vanes defines an intervening flowpassage having an effective minimum flow area, commonly referred to asan exit or throat area, measured within a plane of minimum spacingbetween the trailing edge of one vane and the opposing convex airfoilsurface of the adjacent vane. The nozzle ring as a whole has a totaleffective flow area equal to the sum of the several intervane throatareas. According to conventional design procedure, the turbine designerspecifies the vane airfoil shape, the nominal airfoil angle, and thenoule ring flow area for a particular jet engine design. Afterconstruction, each jet engine is individually tested and tuned foroptimum performance by adjusting the nozzle ring flow area.

Adjustment of the nozzle ring flow area is accomplished, in effect, byvarying the airfoil angles and hence throat areas of the vanes. Thus,rotating the vane airfoils in one direction about their so-calledstacking axes reduces the throat areas and hence the total effectivenozzle ring flow area. Rotating the airfoils in the opposite directionincreases throat area and hence total flow area. As is well known bythose versed in the art, nozzle ring flow area is thus adjusted, not byphysically rotating the vanes, but rather by selecting vanes whose classsurfaces are machined at different angles relative to their airfoilssuch as to orient the latter at different angles relative to the planeof the nozzle ring. When assembling a set of turbine vanes into a nozzlering, the vanes are selected or matched on the basis of their angularrelation between their machined class surfaces and their airfoilsections, in a manner such as to provide the resulting nozzle ring withthe desired flow area.

From the above discussion, it will be understood that a typical turbinevane may be installed in a nozzle ring in a range of angular positionsto achieve the desired aerodynamic and thermodynamic results in thecompleted jet engine. The different airfoil angles at which the vane maybe thus installed and their related throat areas are designated asclasses. More accurately, the class designation of a turbine vanerepresents the throat or exit area of the flow passage define by thevane and a second vane of the same class when assembled on a specifiedcenter spacing. The airfoil angle or class which provides the throatarea used in the theoretical turbine desing is designated as the basicclass.

According to common turbine-vane-manufacturing procedure, a quantity ofturbine vanes of the same basic vane configuration are cast with thebasic class angle. The full range of vane classes are then fabricatedfrom these basic casting by machining their class surfaces to the properangles.

This manufacturing procedure presents one problem with which the presentinvention is particularly concerned. The problem referred to resides inthe fact that while production turbine vanes may be cast with arelatively high degree of accuracy and precision, nevertheless, theycannot be cast to the exact dimensions used in the theoretical turbinedesign. in other words, production turbine vanes almost always exhibitsome deviation in shape and/or size relative to the basic design vane.Typical deviations are oversize or undersize foil thickness and/orlength, or a twist in the airfoil section. Each of these deviationsalters the effective or so-called blocked area of vane and hence bothits throat area and the total nozzle ring flow area in which the vane isinstalled and must be taken into account in the vane classificationprocess.

Thus, consider two perfect vanes of given class, i.e. vanes whosedimensions conform exactly to the nominal vane dimensions used in thetheoretical design, assembled on specified centers. These vanes definean intervening class throat area measured in the plane of minimumspacing between the vane airfoils, which is the plane containing thetrailing edge of one airfoil and intersecting the confronting convexairfoil surface of the opposing vane along a line passing through thepoints of tangcncy of the latter surface with arcs generated aboutspaced points on the trailing edge. The throat between the vanes isbounded along two sides by the trailing edge and convex airfoil surfaceand along its remaining two sides by the confronting inner shoulderfaces of the vane root and tip buttresses.

Assume now that the perfect vanes are replaced by production vanes. Anydeviation in the shape and/or size of the airfoil of either productionvane from those of the perfect vanes increases or decreases, dependingupon the type of deviation, the effective cross-sectional area, commonlyreferred to as blocked area, of the vane and hence the intervane throatarea. For example, oversize airfoil thickness reduces the throat area asmay twisting of the airfoil section. in order to provide the productionvanes with the same throat area and hence class value as the perfectvanes, it is necessary to vary the airfoil angle of one or bothproduction vanes in the proper direction to increase or decrease thethroat area, as the case may be, by the correct amount to justcompensate for the loss or gain of throat area resulting from theproduction vane deformities. This, in turn, requires accuratemeasurement or gaging of the production vanes to determine theirdimensional deviations from the nominal vane dimensions used in thetheoretical design, machining of the class surfaces of the productionvanes to the proper angle to compensate for the deviations, and regagingof the machined vanes to determine their true class value.

This procedure of gaging turbine vanes for this purpose is referred toas prediction and classification gaging. Briefly, the first step of thisprocedure, known as prediction gaging, involves comparison of selectedairfoil dimensions of a production vane with those of a perfect basicclass vane, or master as it is called, to obtain a figure of meritrepresenting the difference in class values of the production vane andmaster resulting from the differences, if any, in their correspondingairfoil dimensions. This figure of merit is then converted to an angleat which the class surface of the production vane must be machined toprovide the finished production vane with a selected class value whichmay be the same as that of the master or some other selected classvalue. The second step of the procedure involves machining the classsurface of the production vane to the angle determined by thepredictiongaging step. The third and final step of the procedure,referred to as classification gaging, involves comparison of theselected dimensions and the angle of the machined class surfaces of theproduction vane and master to obtain the actual or true class value ofthe production vane.

Instruments, known as prediction and classification gages, have beendevised for performing the prediction and classification steps of thegaging procedure outlined above. However, these existing gages sufferfrom certain deficiencies which this invention overcomes. All of thesedeficiencies need not be discussed in detail in this disclosure. Sufiiceit to say, that a particularly serious defect of the existing gagesresides in the fact that they subject the turbine vanes to clampingforces which distort the vanes and thus introduce error into the gagingprocess. Another drawback of the existing gages involves the measurementof the effective airfoil length, that is the spacing between the vaneroot and tip buttresses. I-leretofore, this airfoil length measurementhas been obtained with a separate gaging instrument, thus complicatingand prolonging the overall prediction and classification procedure.

SUMMARY OF THE INVENTION The present invention provides an improvedturbine vane prediction and classification gaging instrument and methodwhich cures the above and other defects of the existing gages. Thepresent gage comprises two major components, to wit, a mechanical gagingfixture and a computer. The gaging fixture receives, in succession, amaster vane and a production vane to be gaged. The fixture haselectrical gaging means for producing electrical gaging signalsrepresenting deviations or deltas between corresponding selectedcritical dimensions of the master and vane. The computer receives thesegaging signals from the fixture, and, in the prediction-gaging mode,converts the prediction-gaging signals to a figure of merit representingthe difference in the class values of the production vane and themaster. In the classification-gaging mode, the computer converts theclassification-gaging signals from the fixture to the true class valueof the production vane.

A particularly unique and important feature of the invention resides inthe fact that no clamping forces of any kind are exerted on theproduction vane or the master during either prediction orclassification. As a consequence, the vanes are not distorted, and theinstrument provides prediction and classification readings of relativelyhigh accuracy and precision.

According to another feature of the invention, the present predictionand classification instrument is arranged to measure or gage all of thecritical vane dimensions, including the effective airfoil length. As aconsequence, the present gaging instrument performs the classificationand prediction-gaging procedure in minimum time with a relatively highdegree of accuracy and precision, thus reducing the overall turbine vaneproduction time and cost.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a perspective view of a turbine vane;

FIG. 2 is a fragmentary side elevation of a jet engine nozzle ringcomposed of a number of turbine vanes like that shown in FIG. 1;

FIG. 3 is an enlarged section taken on line 3-3 in FIG. 2;

FIG. 4 is a rear elevation of the turbine vane in FIG. 1 looking at theconvex side of its airfoil;

FIG. 5a, 5b, 5c are sections through three chord stations A, B, and Cofthe turbine vane in FIG. 4;

FIG. 6 is a front elevation of the present turbine vane prediction andclassification gaging instrument;

FIG. 7 is an elevational view of the right-hand side of the gagingfixture of the instrument;

FIG. 8 is a front view of the gaging fixture looking in the direction ofthe arrow 8 in FIG. 7;

FIG. 9 is a section taken on line 9-9 in FIG. 6;

FIG. 10 is a section taken on line 10-10 in FIG. 6;

FIG. 11 is a section taken on line 11--1 l in FIG. 6;

FIG. 12 is a section taken on line 12-12 in FIG. 7;

FIG. 13 is a detail of one gage of the fixture;

FIG. 13A is a section taken on line 13A- 13A in FIG. 13;

FIG. 14 is a detail of another gage of the fixture;

FIG. 15 is a longitudinal section through a gage transducer;

FIG. 16, is a schematic circuit diagram of the computer of the gaginginstrument; and

FIG. 17 is a schematic circuit diagram of a logic circuit embodied inthe computer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference is made at first toFIG. 1 illustrating a typical turbine vane 10 of the type which is gagedin the present instrument and to FIG. 2 and 3 illustrating a portion ofa jet engine nozzle ring 12 embodying the vanes 10. Each turbine vane l0has tip and root buttresses l4, 16 with flanges 17a, 17b, an interveningairfoil l8, and a longitudinal stacking axis 20. Buttresses l4 and 16have laterally presented edge surfaces 22 and 24 and confrontinglongitudinally presented shoulder faces 26 and 28. Tip buttresses 14 hasa machined locating face 29 on and normal to stacking axis 20.

In the nozzle ring 12, the vanes 10 are assembled side by side with thevane stacking axes 20 extending radially of the nozzle ring. Theassembled vanes are joined by means not shown to provide a rigid annularnozzle ring structure. The adjacent vanes define intervening taperedflow passages 30. Each flow passage is bounded along its two radialsides by the adjacent vane airfoils l8 and along its root and tip endsby the vanes buttress surfaces 26, 28. The cross-sectional area of eachflow passage diminishes in a direction from the leading edges 34 of thevane airfoils 18. Each passage has a minimum cross-sectional areameasured in a plane P of minimum spacing between adjacent vanes. PlanesP contains the trailing edge 34 of one vane and intersects theconfronting convex airfoil surface 36 of the opposing vane along a linepassing through the points of tangency with the surface of circular arcsK generated about the trailing edge as a center. The minimum areaportion 38 of the passage is commonly referred to as a throat and itsarea S the exit area of the vane flow passage 30. One of the tipbuttress surfaces 22 provides a reference surface, or class surface asit is called and designated in the drawings, which seats against amounting or bolting surface, not shown.

As noted earlier, a typical turbine vane may be used in a range ofangular positions to achieve desired aerodynamic and thermodynamiccharacteristics in the completed jet engine. In this regard, it will beobserved in FIG. 3 that rotation of the vanes 10 about their stackingaxes 20 to vary the angle of the vane airfoils 18 relative to the planeof the nozzle ring 12 increases or reduces, depending upon the directionof the rotation, the areas of the vane throats 38. In actual practice,such vane rotation is accomplished, not by physically rotating the vanesabout their stacking axes, but rather by machining their class surface22 at various angles to orient the vane airfoils l8 at various anglesrelative to the nozzle ring plane. The different angles at which vanesof a given design may be used and the resulting throat areas arereferred to as classes. The delta angle between successive classes isconstant, or approximately constant, over the entire class range.According to the conventional jet engine design practice discussedearlier, the engine designer specifies the nominal airfoil angle, centerspacing, and throat area for a nozzle ring vane set. The vane classwhich has this nominal airfoil angle and throat area is referred to asthe basic class, its airfoil angle as the basic class angle, and itsthroat area as the basic class area. The jet engine is initiallyconstructed with a nozzle ring composed of such basic class vanes. Afterconstruction, the engine is tuned by replacing selected vanes by vanesof another class or other classes, as necessary to provide the enginewith the proper nozzle ring flow area for optimum engine operation.

It will also be recalled from the earlier discussion that according toconventional turbine vanes manufacturing practice, the turbine vanes fora particular engine design are initially cast to the basic class angle.The class surface 22 of the castings are then machined to theappropriate angles to provide finished vanes of the full range ofclasses required for engine tuning purposes. Since the throat areabetween two vanes paired on given centers is a function of both theairfoil angle and airfoil dimensions of the vanes, the deviationsbetween the actual airfoil dimensions of the cast production vanes andthe nominal airfoil dimensions of the class vane used in the theoreticalengine design must be taken into account when machining the castings inorder to achieve finished vanes of a desired class.

In this latter regard, assume a pair of perfect vanes of given basicclass, that is a pair of vanes which conform exactly to a theoreticalbasic class vane design, assembled side by side on specified centerswithin a nozzle ring, as in FIG. 3. Being perfect vanes, the latterdefine an intervening throat 3% whose area exactly equals the throatarea of the basic vane class. As sume next that one vane of the vanepair, say the vane whose convex airfoil surface 36 borders the throat,is replaced by a production vane whose airfoil i8 is oriented at thesame basic class angle but has slightly different dimensions and hence adifferent blocked area than the airfoil of the perfect vane. In thiscase, the actual throat area between the production vane and theremaining perfect vane differs from the class throat area by an amountequal to the difference between the blocked areas of the production vaneand the perfect vane. In order to provide the production vane with thebasic class value of the perfect vane or some other selected classvalue, the airfoil of the production vane must be rotated to an angleequal to the airfoil angle of the selected class plus or minus acompensating angle necessary to compensate or correct for the differencein the blocked areas of the perfect basic class vane and productionvane. As noted earlier, this rotation of the airfoil is accomplished,not by physically turning the vane, but by machining its class surface22 at the proper angle.

It will now be understood that the described practice of producingturbine vanes of a full range of classes for a particular jet enginedesign from production vanes that are initially cast to the basic classangle used in a given theoretical design involves the following steps:

I. Gaging the airfoil of each production vane at the basic class angleto determine its dimensional deviations, if any, from the nominaldimensions of the basic class vane airfoil used in the theoreticaldesign;

2. Determining the angle to which the class surface 22 of eachproduction vane must be machined to compensate for such dimensionaldeviations and provide the finished vane with a selected class value;

3. Machining the class surface of each production vane to theappropriate angle; and

4. Gaging each machined production vane to determine its true classvalue.

The above procedure is referred to broadly as prediction andclassification gaging. The first step constitutes a prediction-gagingstep and the last step constitutes a classificationgaging step.

The present invention is concerned with a prediction andclassification-gaging procedure which involves the use of socalled classformulas, referred to later as prediction and classification formulas,that express class value and class difference (figure of merit) in termsof certain critical airfoil and class surface dimensions. According tothis procedure, a perfect vane, or master, is prepared whose criticalfoil and class surface dimensions exactly equal those of the basic classvane used in the theoretical design. The critical airfoil dimensions ofthis master and a production vane are then compared, and the differencesor deltas, if any, in the corresponding dimensions are combined inaccordance with the appropriate class formula (prediction formula) toobtain a figure of merit representing the difference in class values ofthe master and vane resulting from the differences, if any, in theairfoil dimensions. This figure of merit is converted, with the aid ofexisting tables, to a predicted angle at which the class surface of theproduction vane must be machined to provide the finished vane with aselected class value. The above steps constitute the prediction-gagingphase of the gaging procedure. After machining of the class surface ofthe production vane to the predicted angle, the critical airfoil andclass surface dimensions of the master and production vane are comparedand the differences or deltas in the corresponding dimensions arecombined in accordance with the appropriate class formula(classification formula) to obtain the true class value of the vane. Thelatter steps constitute the classificatiomgaging phase of the gagingprocedure.

in connection with this prediction and classification procedure,consider FIGS. 50, b, and Sc which are sections through the airfoil lbof a perfect basic class vane at three chord stations, A, B, and C (MG.4 located at the root end,

center and tip end, respectively, of the airfoil. The points a, b, and cin these figures represent points on the convex airfoil surface 36 atthe respective chord stations located in the throat plane P Thereference characters P and P,, and P represents plane tangent to the:convex airfoil surface at the points, a, b, and c, respectively. Thereference characters P P represent planes parallel to the correspondingplanes P P and P and tangent to the airfoil-trailing edge M at theconcave side of the vane. The reference characters R, S, and T representthe effective airfoil thickness dimensions at the chord stations A, B,and C, respectively, measured between and normal to the correspondingtangent planes 1P..- R P,, P,, lP,, and E The reference character Urepresents the effective length of the airfoil lll i measured betweendetermined points on the confronting buttress shoulder faces 26, 28adjacent the throat plane P Referring now again to the prediction andclassificationgaging procedure discussed above, the critical deltadimensions used in the procedure are the differences or deltas betweenthe following dimensions of the master and the production vane beinggaged: the airfoil thickness dimensions R, S, and T and the airfoillength dimension U. The class formulas in which these dimensions areused to obtain the figure of merit and class value of a production vanevary from one vane design to another and will be discussed presently.Suffice it to say at this point that the above-mentioned deltadimensions which are used in the formulas to obtain the figure of meritand class value of a production vane are hereafter referred to by thereference characters AR, AS, AT, and AU, respectively.

The present invention provides a prediction and classification-gaginginstrument llllll for performing the prediction and classificationgaging procedure outlined above. This gaging instrument includes twomajor components, namely, a gaging fixture 1102 and a computer NM. Thegaging fixture 1102 is equipped with vane-supporting means 1106 andelectrical gaging means lilfi for gaging and generating electricalsignals representing the critical vane measurements or deltas referredto above. The computer 1104 combines these electrical signals inaccordance with the appropriate class formula for the vane being gagedto provide prediction and classification readouts, as explained below.The gaging instrument has two operating modes, a prediction-gaging modeand a classification-gaging mode. In each mode, a master and a cast vaneare gaged in succession in the fixture 1102. At this point, it issignificant to note that an actual master only simulates the basic classvane used in the theoretical design; that is to say, the master isprovided with gaging surfaces which are accurately machined to providethe master with R, S, T, and U dimensions exactly equal to those of thebasic class vane used in the theoretical desing, but the actual overallshape of the master differs substantially from that of the basic vaneconfiguration. However, for simplicity, it will be assumed in thepresent disclosure that the master has a true vane shape. Further, atsome points in the ensuing description, it will be assumed that the vanewhich is illustrated in the gaging fixture 1102 is the master and atother points in the description it will be assumed that the illustratedvane is a production vane to be gaged. The same reference characters andnumerals used in the earlier description of the vane will be applied tothe master, except that the master will be referred to in its entiretyby the numeral ill).

The instrument is initially set in its prediction-gaging mode and themaster it] is placed at its basic class angle in the vanesupportingmeans 106. The instrument is nulled to register a zero figure of meritreadout indicative of the fact that the gaged dimensions and henceeffective blocked area of the master conform exactly to those of thebasic vane configuration used in the theoretical design. The master 10is now replaced by the production vane ill to be gaged and the vane isrocked on its trailing edge 34 through .a position wherein the vane tipchord station C is oriented at the same angle as the master tip chordstation. Rotation of the vane through this position triggers thecomputer 104 to read the R, S, and U dimensions of the vane and registera figure of merit readout representing the difference between the classvalue of the production vane and master resulting from differences inthe hand baseblock 116, just below its notch 133. Transducer 162 has ahousing 166 slidable in the holder 164 and fixed in position bysetscrews 168. Longitudinally movable in the housing is a plunger 170which extends from the upper rear end of the R, S, andU dimensions ofthe vanes. housing. The outer end of the plunger mounts a hardened 1nthe next step of the prediction and classification-gaging roller orwheel 172. Plunger 170 is supported for axial moveprocedure, the figureof merit reading just obtained is conment in the housing 166 by flexure174 and includes a mag verted, with the aid of prepared tables, to anangular value netically permeable core 176. Surrounding the core is anaxirepresenting the angle to which the class surface 22 of the allyadjustable coil 178. A spring 180 seats against one end of productionvane must be machined to provide the finished 10 the coil. A setscrew182 seats against the other end of the coil. vane with a selected classvalue. The production vane 10 is Set screw 182 is threaded in andaccessible externally of the then removed from the gaging fixture 102and its class surface transducer housing 166 for adjusting the axialposition of the machined to the appropriate angle by the conventionalvanecoil relative to the transducer housing and the plunger. Coilmachining technique. 1 5 178 has a center primary winding to beenergized from an AC The gaging instrument 10 is now set in itsclassification-gagsource and two outer secondary windings which arefound and ing mode and the master 1 10 is repositioned at its basicclass connected in the well-known way to provide an output voltage anglein the gaging fixture 102. The instrument is adjusted to signal, whenthe primary winding is energized, representing register the basic classvalue of the master. Thereafter the the relative axial position of thecore and coil and hence the master is replaced by the machined vane 10and the latter is relative axial position of the transducer plunger 170.Thus, the rocked through successive positions wherein its tip chordstatransducer produces a zero or null output when the core occution Cand then its class surface 22 are oriented at the same pies its centeredor null position relative to the coil 178, and angles as those of themaster. Rotation of the vane through an output voltage which varieslinearly with axial displacethese positions triggers the computer toread and store the U- ment of the core from its null position. Theoutput voltage has dimension, then read the R-, S-, and T-dimensions,and finally 25 one phase relative to the excitation voltage when thecore discompute and register the true class value of the machinedplacement is to one side of the null position and an opposite vane.phase when the core displacement is to the opposite side of The gagingfixture 102 comprises a horizontal baseplate 112 the null position.having supporting legs 114. Fixed side by side to the upper Gages 154,155 are essentially identical to gage 152 and surface of the baseplateare three triangular baseblocks 116, hence need not be described indetail. Suffice it to say that 118, and 120 with sloping front faces116A, 118A, and 120A. gages 154, 155 include electrical transducers 184,185 ad- The front faces of the two outer blocks, 116, 120, have alignedjustably mounted in holders 186, 187 bolted to the front faces notches122. 118A, 120A of baseblocks 118, 120. The transducer plungers Thevane-supporting means 106 of the fixture comprise a 188, 189 extend fromthe upper rear end of the transducer pair of essentially identical vanesupports 124 on the two outer housings 190, 191 and mount hardenedrollers or wheels 192, base blocks 116, 120. Each support comprises achannel- 193. The transducer coils are adjustable relative to thehousshaped bracket 126 which is bolted to the block front face just ingsand plungers by setscrew 194, 195. above the block notch 1226, with theaxis of the channel ex- Gage 156 is also similar to gage 152 andincludes an electritending lengthwise of the face. Slidable in eachchannel cal transducer 198 adjustably mounted in a holder 200 boltedbracket 126 is a bar 128. A clamp plate 130 extends across the to thefront face 118A of baseblock 118 above and directly top of each bracketand is attached to the latter by bolts 132. opposite gage 154. The upperportion of the block face 118A These bolts may be tightened to clamp thebar 128 in fixed supporting the gage 156 is stepped downwardly relativeto the position within the bracket. The front or lower end of thesuplower portion of the block face supporting the gage 154. This portbar 128 has an upper recess 134 which exposes the stepped configurationof the block face locates the gages 154, abutting ends of a pair ofhardened pins 136, 138 press fitted 156 in laterally offset relation, asshown, for reasons to be exin the bar. Pin 136 extends parallel to thelongitudinal axis of plained presently. Transducer 198 includes aplunger 202 the bar. Pin 138 extends perpendicular to the bar axis andwhich extends from the lower end of the transducer housing hence to thepin 136. Accordingly, the pins 136, 138 on each 204 and terminates in ahardened tip 206. At the upper end of support bar 128 define aright-angle comer 140, or trap as this the housing is a setscrew 208 foradjusting the transducer coil comer is hereinafter referred to. As willappear presently, the relative to the housing and plunger. As will beexplained traps 140 of the vane supports 124 seat the trailing airfoilpresently, the vane gages 152, 154, 155, and 156 are arranged edges 34of the production vane 10 being gaged and the to contact the vanecurrently positioned in the fixture at its master 110. Threaded in theouter end of each bar 128 is a set root, center, and tip chord stationsA, B, and C. Gages 152, screw 142 which seats against the rear wall ofthe adjacent 154, 155, and 156 gage the AR, AS, and AT vanemeasurebaseblock notch 122 to vertically support the bar end againstments, referred to earlier. downward deflection. The set screws areadjustable to provide Gage 158 gages the AU vane measurement andcomprises this support in every position of adjustment of the bars 128an electrical transducer 210 essentially identical to the other relativeto their channel brackets 126. transducers. Thus, the transducer 210 hasthe plunger 212 As noted earlier, and explained in greater detail in theensuwhich extends axially from one end of the transducer housing ingdescription, the master 110 and production vane 10 are 213 andterminates in a threaded end 214. A setscrew 216 is placed in the traps140 successively. For convenience in this exposed at the opposite end ofthe housing for adjusting the ensuing description, both the productionvane and the master transducer coil. Transducer 210 is loosely receivedin aligned will be referred to, in places, simply as vanes. When a vaneis bores 218 extending through the base blocks 116, 118, and seated inthe traps, its airfoil 18 projects laterally out from the 120 parallelto the .baseplate 112 and normal to the axes of the base blocks 116,118, and 120 with the convex airfoil surface gages 152, 154, 155 and156. 36 facing the lower ends of these faces. The outer baseblock Inaddition to the transducer 210, gage 158 includes a pair notches 122provide clearance for the vane buttresses 14, 16, of gage arms 220, 221positioned within aligned grooves or as shown. It will be observed thatthe traps accommodate recesses 222, 223 in the outer baseblocks 116,120. The translimited pivotal movement of the vane about its trailingedge. ducer bore 218 opens to the recesses, as shown. The lower Theelectrical gaging means 108 of the gaging fixture 102 ends of the gagearms 220, 221 are hingably attached by flexcomprise six electrical gages152, 154, 155, 156, 158, and ures 224, 225 to blocks 226, 227 fixedWithin the lower ends 160. Gage 152 includes an electrical linearvariable difof the recesses 222, 223. The transducer body 213 extendsferential transformer or transducer 162 mounted in a holder through andis fixed to arm 2 20. The threaded end 214 of the 164,. This holder isbolted to the front face 116A of the lefttransducer plunger 212 extendsthrough and is fixed to arm 221. Fixed in and projecting outwardly fromthe upper ends of the arms 220, 221 are hardened gage pins 234, 236.Gage pins 234, 236 are located on a common axis R parallel to the axisof transducer 210 and are arranged to seat against the inner shoulderfaces 26, 211 of the vane buttresses 14B, 16.

The remaining gage 160 is arranged to gage the angle of the vane classsurface 22 and has a novel construction which is uniquely adapted tothis function. Gage 160 comprises a transducer 2 16 mounted in a holder24% in the form of a rectangular block. Holder 248 is attached by a pairof flexures 250 to a mounting bloclc 252 bolted to the outer right-handface of the right-hand bweblock 126. Bolted to the inner surfaces of theflexures 250 are rigid plates 251. In the normal position of the gage,the flexures 2511 are parallel to one another and normal to the axis ofthe gage transducer 246. These flexures have equal effective lengthsmeasured between their points of attachment to the transducer holder 248and mounting block 252. Also, the points of attachment at each end ofthe flexures are aligned in a direction parallel to the transducer axis.Finally, the plates 256 have equal length somewhat less than theeffective flexure lengths and are centered between the points of flexureattachment. From this description, it will be understood that theflexure support 250, 25 1 effectively forms a parallelogram spring mountfor the transducer 266 which supports the latter for translationalmovement along its axis. Mounting block 252 has a reduced extension 256projecting between the fiexure plates 256 for limiting translationmovement of the transducer. Acting between the holder 2418 and a bracket253 attached to the mounting block 252 is a compression spring 260.

Transducer 256 is essentially similar to the transducers 156, 153 andincludes a housing 262 adjustably secured within the holder 24%. Fixedto the upper end of the transducer plunger 26 1 is an arm 265 whichprojects laterally through a slot 265a in holder 24% and mounts a hardpin 266. A setscrew 265 adjusts the transducer coil. Holder 266 has abracket arm 270 in which is threaded a hard pin 272 aligned with pin 266in the fore-andaft direction of the fixture. As may be best observed inFIG. 13A, gage pins 266, 272 are located within the notch 122 inbaseblock 120). It will now be understood that the flexures 250 supportthe gage transducer 246 and gage pin 272 for axial translation inunison. The transducer plunger 264 is also axially movable independentlyof the gage pin 272.

As noted earlier, the present gaging instrument 101) is used forpracticing a prediction and classification-gaging procedure wherein theR, S, and U dimension of a production vane and master 110 are comparedand the dimensional differences, if any, are combined according to aprediction formula to obtain a figure of merit representing thedifference in the class values of the vane and master. This figure ofmerit is then converted to an angle to which the class surface 22 of theproduction vane must be machined to provide a finished vane of thedesired class value. After machining of the surface, the R, S, T, and Udimensions of the vane and master are compared and the dimensionaldifferences are combined according to a classification formula toprovide a readout representing the true class value of the vane.

To this end, the gaging fixture 102 is designed to receive, in theillustrated gaging position, both the production vane 10 to be gaged andthe master vane 110. In this gaging position, the root end of the vanecurrently positioned in the fixture, i.e. either the cast vane or themaster, is located at the left-side of the fixture as the latter isviewed from the front. The trailing edge 31 of the vane airfoil 18 restsin the traps 146 with the trailing edge seating downwardly against thetrap pins 136 and rearwardly against the trap pins 136. The wheels 172,192, and 193 of the vane gages 152, 1, and 155 engage the convex airfoilsurface 36 at positions spaced along the airfoil 16. The plunger tip 206of the vane gage 156 engages the vanetrailing edge 36 at the concaveside of the airfoil 16. The gage pins 234, 236 of the vane gage 158 seatagainst the confronting root and tip buttress shoulder faces 26, 28,respectively. Finally, the gage pins 266, 272 of the vane gage 160 seatagainst the confronting tip buttress class surface of the vane.

The two pins 136, of each vane trap 160 are perpendicular to one anotherand located in a common plane P normal to the common axis R of the gagepins 236, 236. The two planes P which are hereafter referred to as trapplanes, are spaced a distance equal to the spacing between the root andtip chord stations A, C of the vanes to be gaged. The wheel 193 of thevane gage is located! in the right-hand or tip trap plane P as thegaging fixture is viewed from the front. The wheel 172 of the left-handvane gage 152 is located in the left-hand or root trap plane P The wheel192 and the plunger 202 of the center vane gages 1541-, 156 are locatedin a common plane between and parallel to the trap planes, and spacedfrom the trap planes distances equal. to the spacing between the centerchord station B and the root and tip chord stations A, C of the vanes tobe gaged.

The vane traps 1 10 are so arranged that when the trailing edge 34 of avane is properly seated in the traps, its stacking axis 20 is parallelto the common axis R of the gage pins 234, 236 and perpendicular to thetrap planes P Accordingly, the chord planes of the three vane chordstations, A, B, and C are then perpendicular to the axis R and parallelto the trap planes P A fixed bracket 273a mounts screws 27312, 273:-which are engageable with the vane flange 17a and locating face 29, asexplained shortly, to locate the vane endwise in a position wherein thechord planes of the root and tip chord stations, A, C of the vanecoincide with the two trap planes P The center vane gages 154i, 156 areso located that the common plane of the gage wheel 192 and gage plunger202 coincides with the plane of the center vane chord station B. Thus,the wheels 172, 192 of the vane gages 152, 1541 contact the convexsurface 36 of the vane airfoil 18 at its root and center chord stationsA, B, respectively. The Wheel 19 3 of the vane gage 155 contacts theconvex airfoil surface at its tip chord station C. The plunger 202 ofthe vane gage 156 contacts the trailing edge of the airfoil at itscenter chord station B.

As explained later, during gaging operation of the instrument, themaster 110 is placed in the fixture 102 at its basic class anglerelative to the fixture baseplate 112. In this position the master classsurface parallels the baseplate and the master airfoil is oriented atthe basic class angle relative to the baseplate. The master trailingedge 34! then coincides with a trap axis passing through the right anglecorners of traps 1410.

From the earlier discussion relative to F168. 50, 5b, and So it will berecalled that points a, b, and 0 represent points on the convex airfoilsurface 36 at the chord stations, A, B, and C located in the throatplane P of the vane. In other words, points a, b, and c are the pointsof tangency, at the chord stations A, B, and C of the convex airfoilsurface with circular arcs (i.e. arcs K in FIG. 3) generated about thetrailing edge 341 of an adjacent vane. Assuming the illustrated vane tobe a perfect vane or master 110, the arcs which define the tangencypoints a, b, and c have predetermined radii R R,, and R equal the widthof the vane throat 36 at the chord stations A, B, and C, respectively,and are hereafter referred to as throat width dimensions. The R, S, andT dimensions are effective airfoil thickness dimensions measured betweenand are normal to the respective tangent plants P,, P,, P,, P,, P andP,. The U-dimension is the effective airfoil length dimension measuredbetween the confronting buttress shoulder faces 26, 26 approximately inthe throat plane P The vane gages 152, 154i, and 155 are so constructedand arranged on the fixture 162 that when the master 110 occupies itsbasic class angle or gaging position in the fixture, with the gagewheels 172, 192, and 193 in contact with the master airfoil 18, thewheel centers are located on a common axis which parallels the trap axisdefined above and these axes occupy the same relative positions as dothe trailing edges 34 of two adjacent perfect vanes or masters 110 whenassembled in the manner of FIG. 3. The wheel 193 of gage 155 has aradius equal to the throat width dimension R, at the tip chord station Cand contacts the convex airfoil surface 36 of the master at its tipchord station tangency point e. The longitudinal axis of adjustment ofthe adjacent vane trap support bar 126 and the axis of the gage plunger139 are perpendicular to a plane P tangent to the gage wheel 193 at itspoint of contact with the master foil surface 36. The frontvane-engaging side of the adjacent trap pin 138 is located in a plane Pnormal to the bar axis and parallel to the tangent plane P The wheel 172of the vane gage 152 has a radius equal to the throat width a, R, at theroot chord station A of the master and contacts the convex airfoilsurface 36 of the master at its root chord station tangency point a,when the master occupies its gaging position. The longitudinal axis ofthe plunger 170 of the gage transducer '162 is perpendicular to a planeP,, tan gent to the gage wheel 172 at its point of contact with theairfoil surface 36. The longitudinal axis of adjustment of the adjacentvane trap support bar 128 is perpendicular to the latter tangent planeP,, The front vane-engaging side of the adjacent trap pin 138 is locatedin a plane P, perpendicular to the latter support bar axis and parallelto the tangent plane P,,

The wheel 192 of the vane gage 154 has a radius equal to the throatwidth dimension R, at the center chord station B of the master andcontacts the convex airfoil surface 36 of the master at its center chordstation tangent point b when the master occupies its gaging position inthe fixture. The longitudinal axis of the plunger 188 of the gagetransducer 154 is perpendicular to a plane P tangent to the gage wheel192 at its point of contact with the airfoil surface 36. Thelongitudinal axis of the plunger 202 of the gage transducer 156 isperpendicular to the latter tangent plane. The end vane-engaging face ofthe plunger tip 206 is located in a plane P perpendicular to the plungeraxis and parallel to the tangent plane b-ll- As noted earlier, the gagepins 234, 236 of the vane gage 158 have a common axis R which is normalto the trap planes P and parallel to the stacking axis 20 of the master1 10 when the latter occupies its gaging position in the fixture 102.The gage pins are mounted on the fixture to contact the buttressshoulder faces 26, 28 of the master at the points on these faces betweenwhich is measured the airfoil length dimension U in FIG. 4.

Referring to FIG. 13, it will be seen that the remaining gage 160 ismounted on the gaging fixture 102 so that its gage pins 266, 272 arenormal to the adjacent class face 22 of the tip buttress 14 of themaster 110 when the latter is in gaging position. The plunger and pinare laterally spaced a predetermined distance approximating the lengthof the face so that the plunger and pin contact the face adjacent itsends. In this regard, it will be observed that the gage pin 272 isretained in seating contact with the class face by the gage flexures 250and spring 260. The gage 266, on the other hand, is retained in seatingcontact with the class face by .the conjoint action of the gage flexures250, spring 260, and the fiexure 174 in the gage transducer 246.

From the description to this point, it is evident that when a vane(either a production vane 10 or the master 1 10) is placed in gagingposition in the gaging fixture 102, the perpendicular spacing betweenthe planes P P,, in FIG. 9 equals the effective airfoil thickness R(FIG. a) of the vane at its airfoil root chord station A. Accordingly,since the vane traps 140 are fixed during the gaging operation, theaxial position of the transducer plunger 170 of vane gage 152 isrelated'to the effective airfoil thickness R. Similarly, theperpendicular spacing between the planes P, P, in FIG. 10 equals theeffective airfoil thickness S (FIG. 5b) at the center chord station B ofthe vane. The relative axial positions of the transducer plungers 188,202 of vane gages 154, 156 are thus related to the airfoil thickness S.Finally, the perpendicular spacing between the planes P P in FIG. 10equals and the axial position of the tip gage plunger 189 is related tothe effective airfoil thickness T (FlG. 5c) at the tip chord station Cof the vane. The gage pins 234, 236 of the vane gage 158 seat againstthe inner confronting faces 26, 28 of the root and tip buttresses 14, 16of the vane. The relative axial positions of the plunger 212 and body213 of the gage transducer 210 is thus related to the airfoil lengthdimension U in FIG. 4. The gage pins 266,

272 of the remaining gage 160 seat against the tip buttress class face22 of the vane. The relative axial positions of the plunger and pin isthus related tothe angle of the class face relative to the baseplate112.

The operation of the gaging fixture 202 will now be described. As notedearlier, the present gaging instrument has two gaging modes, to wit, aprediction-gaging mode and a classification-gaging mode. In theprediction-gaging mode, the master is initially fixed in any convenientmanner in its basic class angle gaging position in the fixture, and thetransducers of the vane gages 152, 154, 155, 156, 158, and are nulled byaxially adjusting their coils relative to their plungers. In thisregard, it will be recalled that such transducer has a coil-adjustingscrew. lt should also be noted here that the transducers are energizedfrom an AC power supply, to be described presently, and that computer104 is equipped with means for reading the output voltage of eachtransducer to permit nulling of the transducers. Suffice it to say atthis point that when the transducers have been properly nulled, eachtransducer produces a null or zero output voltage.

A production vane 10 is now placed in the fixture and is rocked fore andaft in the traps 140, about the vane-trailing edge 34, through the nullposition of the T-gage transducer 185. As explained later, rotation ofthe vane through this position triggers the computer 104 to read theoutput voltages, if any, of the R, S, and U gages 152, 154, and 158.Thus, transducer 162 of the root vane gage 152 produces an outputvoltage proportional to the difference AR in the effective airfoilthickness dimension R at the root chord station A of the vane andmaster. The transducers 184, 198 of the center vane gages 154, 156produce output voltages whose sum or difference, depending upon whetherthe transducer coils are wound in the same direction or in oppositedirections, is proportional to the difference AS in the effectiveairfoil thickness dimension S at the center chord station B of the vaneand master. In the particular embodiment of the invention illustrated,the center gage transducer coils are wound in such a way that thedifference between the transducer output voltages is proportional to thedifference AS in the effective airfoil thickness dimension S at thecenter chord station 13 of the vane and master. In the particularembodiment of the invention illustrated, the center gage transducercoils are wound in such a way that the difference between the transduceroutput voltages is proportional to the difference AS in the airfoilthickness dimension S of the production vane and master. Finally, thetransducer 210 of the vane gage 158 produces an output voltageproportional to the difference AU in the effective airfoil lengthdimension U of the vane and master. The output voltage of the remainingclass face transducer 160 is not involved in the predictionclassification mode of the instrument. In the prediction mode, the vanelocator screw 2730 is threaded in to engage its head with bracket 273aand its tip with the vane locator face 29. This screw locates both themaster and production vane in the proper longitudinal position relativeto the gages during prediction and remains in contact with the locatorface 29 of the production vane throughout its rocking angle. It willappear presently that the above AR, AS, and AU dimensions to which thegage output voltages are proportional are the same AR, AS, and AUdimensions which are included as terms of the prediction formulamentioned earlier. As will be explained presently, the computer 104 ofthe gaging instrument combines the AR, AS, and AU output voltages of thegages 152,, 154, 156, and 158 in the prediction-gaging mode according tothe prediction formula for the particular vanes being gaged and producesa figure of merit readout representing the difference in the classvalues of the production vanes and master. This figure of merit readoutis then converted, with the aid of existing conversion tables, to anangle at which the class face 22 of the production vane must be machinedto provide the finished machined vane with a selected class value. Theclass face of the vane is then machined to that angle by existingvane-machined techniques.

In the classification-gaging mode of the gaging instrument, the master110 is replaced in gaging position in the gaging fixture 102 and thelocator screw 273c is retracted and screw 273b is threaded in to engageits head with bracket 273a and its tip with the master flange 1% tolocate the master, and later the production vane, in the properlongitudinal position relative to the gage. The null condition of eachvane gage 152, 154, 155, 156, 155, and 1611 is checked andreestablished, if necessary. The machined production vane 16 is thenreplaced in the fixture and the vane is rocked first through the nullposition to the T-gage transducer 155 and then through the null positionof the class surface gage transducer 2416, hereafter referred to as aW-gage transducer. As explained later, the computer 104 is triggered toread and store the AU output of the U-gage transducer 216 in response torotation of the vane through the T-gage null position. Rotation of thevane through the W-gage null position triggers the computer to read theAR, AS, and AT outputs of the R, S-, and T-gate transducers 162, 164i,165, and 1911, then combine these latter outputs with the stored AUoutput according to classification formula for the vane, and finallyproduce a readout representing the true class value of the vane. Thelocator screw 2731b contact the flange 17b of the vane throughout itsrocking angle.

Relative to the class surface or W-gage 1611, it is evident that itstransducer 246 produces an output proportional to the difference in theclass face angles of the production vane and master at any given angleof the vane. In this latter regard, consider H6. 13 wherein it will beobserved that the gage plunger 264i assumes one fixed axial positionrelative to the transducer body 262 when the master 110 is in gagingposition in the fixture 102. As noted earlier, the master class surfaceis then parallel to the fixture baseplate 112. The gage transducer 246is nulled in this position of the plunger. When the production vane 111is placed in gaging position in the fixture, the angle of the machinedclass face 22 of the vane relative to the fixture baseplate 112. if thevane class face is precisely parallel to the baseplate, the plunger 266will occupy its null position relative to the transparent body 262 andthe gage 166 will produce a null output. On the other hand, if the classface of the is disposed at some oblique angle relative to the baseplate,the transducer plunger 26 1will be displaced axially from its nullposition with respect to the transducer body 262 and the gage 1611 willproduce an output voltage. Accordingly, rotation of the vane 16 throughthe position in which its class surface 22 parallels the baseplate 112is signalled by a null output of the gage 1611. This null outputtriggers the computer 1 to read the AR, AS, and AT outputs and computethe true class value of the vane as mentioned above and describedpresently.

Turning now to H0. 16, the computer 164! of the gaging instrumentincludes an amplifier-demodulator 3611 connected to the output of thetransducer of each fixture gage 152, 154, 155, 156, 153, and 160. Theseveral transducers and amplifier-demodulators are connected throughleads of an electrical cable 302 extending between the computer and aterminal box 3641 on the rear of the gaging fixture 1112. The outputs ofthe amplifier-demodulators 31lil'are connected through leads 3116 tosuccessive fixed contacts of a rotary selector switch 310 and throughleads 312 to corresponding ends of separate voltage dividers 3M. Eachvoltage divider has a tap 316 connected to the input of a bufferamplifier 318. The outputs of the buffer amplifiers for gages 152, 154,155, and 156 are connected through summing resistors 320, a common lead322, and a relay 323 to the input of a summing amplifier 326. The outputof the buffer amplifier for gage 158 is connected to the summingamplifier through a relay 3241, a sample/hold circuit 326, a summingresistor 320, the common lead 322, and the relay 323. The output of thesumming amplifier is connected to its input through a feedback circuit327 and to one fixed contact of the selector switch 310. A readoutdevice 328, such as a digital voltmeter, is connected to the rotarycontact of the switch. The outputs of the buffer amplifiers for fixturegages 155, 166 are connected to a control circuit 330 which operates therelays 323, 325 and feed a strobe signal to the voltmeter 326 inresponse to certain gaging system conditions, as explained shortly. Forreasons which will appear from the later description of the controlcircuit 330, it is necessary during initial operation of the instrumentto disconnect the circuit from the relays 323, 325 and to operate thedigital voltmeter 326 without the aid of strobing signals from thecontrol circuit. Disconnection of the relays is accomplished by openingrelay disconnect switches 331 between the relays and the controlcircuit. This permits the relays to remain in their illustrated normalpositions wherein the upper relay contacts are closed to connect thebutter amplifier outputs to the summing amplifier 326 and to thesample/hold circuit 326. The digital voltmeter used is one having meansfor switching its operating mode between a self-strobing or internalstrobing mode and an external strobing mode. in its internal strobingmode, the voltmeter displays input voltages fed to it through theselector switch 316 without the aid of strobing signals from the controlcircuit 3311. in its external strobing mode, the voltmeter displaysinput voltages only in response to strobing signals from the controlcircuit.

Also included in the computer 1116 are two fixed DC voltage sources 332,3341. These voltages sources are connected to the summing amplifier 324through variable resistors 336, 338 and a selector switch 3410. Voltagesources 332, 334i produce DC voltages of equal fixed magnitude butopposite polarity.

Electrical power for the computer 10 1 of the present gaging instrumentis furnished by a suitable power source which has been omitted from thedrawings for the sake of clarity. This power supply also powers anoscillator which is connected to the center primary windings of thetransducers of the several vane gaging 152, 15 1, 155, 156, i, and andfurnishes the excitation voltages for the transducers.

Turning to FIG. 7 it will be seen that the computer 104 has a housing34141 with a front control panel 346. Switches 310, 331, and 3410 havemeans on the panel by which the switches may be moved to their variouspositions. Readout device or digital voltmeter 323 has a visual readoutdisplay 354 on the panel.

Selector switch 310 has a gaging position and five additional positionswhich are hereafter referred to as calibration positions. in its gagingposition, the switch connects the output of the summing amplifier 32 1to the digital voltmeter 328. Rotation of the switch through itscalibration positions connects the outputs of the amplifier-demodulators300 in succession to the voltmeter. Selector switch 341) has predict andclassify positions. In its predict position, the switch connects the DCvoltage sources 332, 334 to the input of amplifier 324 through resistor336, hereafter called a predict trim resistor. in its classify position,the switch connects the DC sources to the input of the summing amplifierthrough the variable resistor 336, hereafter referred to as a classvalue resistor.

From the foregoing description of the computer 1114, it will beunderstood that the transducers of the vane gages 152, 154, 155, and 156are connected to the input of the summing amplifier 32 1 through theirrespective amplifier-demodulators 3116, voltage dividers 314, bufferamplifiers 313, and the common lead 322, the transducer of vane gage 158is connected to the summing amplifier through its amplifier-demodulator,voltage divider, buffer amplifier, and its sample/hold circuit 326, andthe output of the amplifier is connected to the voltmeter 325. Rotationof the selector switch to any one of its five calibration positionsconnects the output of the amplifierdemodulator 3 06 for one of the vanegages 152, 154, 155, 156, 156, or 160, depending upon the calibrationposition, directly to the digital voltmeter 323.

Operation of the gaging instrument involves three basic steps, a firstcalibration step, a second prediction-gaging step, and a finalclassification-gaging step. in the initial calibration step, the digitalvoltmeter 328 is switched to its internal strobing mode and the relaydisconnect switches 331 are opened. The master 110 is fixed in anyconvenient manner in its basic class angle position in the gagingfixture 102. The transducers of the gages 152, 15 1, 155, 156, 158, and160 are then nulled in succession by rotating the selector switch 310 tothe appropriate calibration positions and adjusting the coil-adjustingor calibration screws 182 of the transducers until the voltmeter 328registers a null reading. The selector switch 310 is then rotated to itsgaging position and the selector switch 340 to its predict position.Under these conditions, the bufier amplifiers 318 for the gages 152,154, 155, 156, and 158 and the DC sources 332, 334 are connected to theinput of the summing amplifier 324 and the output of the summingamplifier is connected to the digital voltmeter 328. The predicttrimming resistor 336 is then adjusted to obtain a null reading on thedigital voltmeter. This trimming resistor is provided to null out anystray voltages resulting from slight unbalances in the system. At thispoint, then, the instrument displays a null condition in which the gagetransducers all produce null outputs and the digital voltmeter registersa null readout. After completion of the above procedure, the selectorswitch 340 is placed in its classify position and the class valueadjustment resistor 338 is adjusted to obtain on the digital voltmeter areadout equal to the basic class value of the master 110. Thecalibration step is then completed by switching the voltmeter to itsexternal strobing mode, closing the relay disconnect switches 331, andremoving the master from the gaging fixture 102.

ln the prediction-gaging mode of the instrument, a production vane 10with an unmachined class surface is placed in the fixture 102 and thevane is rocked forwardly, i.e. toward the front of the fixture, to aforward limiting or reset position and then rearwardly. From the earlierdescription of the fixture 102, it will be understood that during thisrocking of the vane, the latter rotates in the fixture traps 140 aboutthe trailing edge 34 of the vane and that the transducer plungers of thegages 152, 154, 155, 156, 158, and 160 are retained, by the transducerflexures 174, in yielding contact with and thereby follows the vanethrough out its range of rocking motion. in other words, the plungersmove in and out of their transducer bodies as the vane is rocked backand forth.

Initial forward rotation of the vane 10 is continued through the nullposition of the T-gage transducer 185 to the forward reset positionwhich is located slightly beyond or forwardly of the latter nullposition. AS will appear from the later description of the controlcircuit 330, the output from the T-gage transducer 185 in the resetposition triggers the circuit to illuminate a start test lamp 346,indicating to the operator that the reset position has been reached, andresets a digital logic system embodied in the control circuit.

Subsequent rearward rocking of the vane 10 from its forward resetposition is continued until the vane rotates back through the nullposition of the T-gage transducer 185, wherein the transducer produces anull output. In the later description of the control circuit 330, itwill be explained that this null signal from the transducer 185 triggersthe circuit to operate the relays 323, 325 from their illustrated normalpositions, thereby opening the upper relay contacts and closing thelower contacts, and to feed a strobe signal to the digital voltmeter328. These actions cause the voltmeter to display a figure of meritreadout representing the difference in the class values of the masterand production vane resulting from the differences, if any, in their R,S, and U dimensions.

In order to understand how this figure of merit readout is produced,consider the conditions which exist at the instant the production vanepasses through, i.e. occupies, the T-gage null position referred toabove during rearward rocking of the vane from the forward resetposition. In this null position, the tip chord section C of the vane isobviously oriented at the same angle relative to the fixture baseplate112 as was the tip chord section of the master during initial nulling ofthe instrument with the master fixed in its basic class angle positionin the fixture. Accordingly, at the instant the production vane occupiesits T-gage null position, the transducers of the R, S-, and U-gages 152,154, 156, and 158 produce output voltages representing the differencesin the R, S, and U dimensions of the master and vane, i.e. the AR, AS,and AU dimensions referred to earlier, as measured at the T-gage nullposition. More specifically, the output voltage of gage 152 representsthe AR dimension, the difference in the output voltages of the gages154, 156 represents the AS dimension, and the output voltage of the gage158 represents the AU dimension. As will appear from the laterdescription, the above AR, AS, and AU dimensions constitute thevariables of the prediction formula which is used to compute thedifference in class values of the master and production vane, i.e. thefigure of merit of the vane, in the prediction gaging mode of theinstrument.

These gage output voltages are amplified and demodulated in theamplifier-demodulators 300 to produce DC voltages representing the abovedimensional deviations AR, AS, and AU of the production vane at theT-gage null position. The DC voltages from the amplifier-demodulatorsare applied to the corresponding voltage dividers 314. Each voltagedivider is set to produce an output voltage equal to the product of itsrespective input voltage and a constant determined by the class formulaof the vanes being engaged, as explained presently. The output voltagesfrom the voltage dividers are amplified in the buffer amplifiers 300 andapplied to the input of the summing amplifier 324along with the outputvoltage from the prediction trimming resistor 338. As explained below,the null output from the T-gage 155 at the instant the vane 10 passesthrough the T-gage null position triggers the control circuit 330 tooperate relays 323, 325 and feed a strobe signal to the voltmeter 328.These actions cause the summing amplifier 324 to produce an outputvoltage proportional to the algebraic sum of the several amplifier inputvoltages, which output voltage is applied to the digital voltmeter 328,and the voltmeter to display a figure of merit readout representing thedifierence on the class values of the production vane and master. Thisfigure of merit is converted, with the aid of existing charts or tables,to an angle at which the class face 22 of the production vane must bemachined to produce the finished machined vane with a selected classvalue which may be either that of the master or some other class value.

In connection with the above gaging procedure, it is significant torecall that the production vane 10 does not remain stationary in theT-gage null position, but rather passes through this position during itsrearward rocking motion from the forward reset position. Accordingly,the AC output voltages from the gage transducers, and hence the DCvoltages fed to the summing amplifier 324 from the buffer amplifiers318, continuously change and represent the AR, AS, and AU dimensions ofthe vane only at the instant of passage of the vane through the T-gagenull position. Connected between the output and input of the summingamplifier 324 is a condenser 348 which is continuously charged to thevarying input voltage level to the amplifier. The sample/hold circuit326 for the U- gage 158 includes a summing amplifier 350 whose input isconnected to the corresponding buffer amplifier 318 through the uppercontact of relay 325 and whose output is connected through thecorresponding summing resistor 320 to the common lead 322. Connectedacross the input and output of the summing amplifier 350 is a condenser352 which is continuously charged to the varying input voltage level tothe amplifier from the Ugage buffer amplifier.

From this description, it will be understood that at the instant ofpassage of the production vane 10 through the T-gage null positiondescribed above, the condensers 348, 352 are charged to the inputvoltage levels to their respective amplifiers at that instant. Thecharge on the condenser 352 then represents the product of the AUdimension of the production vane (measured at the T-gage null position)and the class formula constant represented by the setting of thecorresponding voltage divider 314. The charge on the condenser 348represents the sum of the prediction trimming resistor output voltageand the products of the AR, AS, and AU dimensions (measured at theT-gage null position) and the respective class formula constantsrepresented by the settings of the corresponding voltage dividers 314.

As will appear from the later description of the control circuit 330,the null signal from the T-gage transducer 185 upon rearward rotation ofthe vane through the T-gage null position triggers the control circuitto operate the relays 323, 325 from their illustrated normal positions,thereby opening the upper relay contacts and closing the lower contacts,and to feed a strobe signal to the digital voltmeter 328. These actionsisolate the summing amplifier 32A from the buffer amplifiers 318 andilluminate a test complete lamp 350 to signal completion of theprediction gage step, and actuate the voltmeter to display a readingrelated to the voltage level of the charge then stored in the summingamplifier condenser 348. This voltage level is obviously equal to theinput voltage to the summing amplifier 324 at the instant the vane 10passes through its T- gage null position. In other words, the summingamplifier 32d and its condenser 348 provide a sample/hold circuit whichstores the input voltage sum to the amplifier at the T-gage nullposition. The digital voltmeter 328, when activated by the moderepresents the difference in class values of the master and vane and isdisplayed as a corresponding numerical figure of merit readout on thevoltmeter 328.

it will be understood from the above description of the sample/holdcircuit 326 for the U-gage 158 that the latter is isolated from itsbuffer amplifier 318 upon operation of relay 325 by control circuit 330at the T-gage null position. This latter sample/hold circuit theoperates in essentially the same manner as the sample/hold circuit 324,338, to store its buffer amplifier input voltage at that instant andfeed this stored voltage to the summing amplifier 322 along with thevoltages from the buffer amplifiers for the gages 152, 154, and 156.

After being gaged in the manner explained above, the production vane 10is removed from the gaging fixture 102 and the class surface 22 of thevane is machined to the angle corresponding to the figure of meritreadout obtained in the above prediction step and desired class value ofthe machined vane. In this regard, it will be recalled that themachining angle is obtained from prepared tables or charts which listthe proper class face angles for various figures of merit and classvalues. This conversion of figure of merit to class face angle and thetechniques used to machine the vane class face to the resulting angleare well known and do not constitute a part of the present invention.Accordingly, it is unnecessary to discuss the same in the presentdisclosure.

in the final classification gaging step of the gaging instrument, themaster 110 may be replaced in its basic class angle position in thegaging fixture 102 and the mode selector switch 310 stepped through itscalibration positions to make certain that the transducers of the vanegages 152, 154, 155, 156, 158, and 160 are still in their nullconditions. Any transducer which provides other than a null reading onthe voltmeter 328 is renulled in the manner explained earlier. Theselector switch 340 is then rotated to its classify" position and theclass value adjustment resistor 338 is adjusted if necessary to obtainon the voltmeter readout display 354 a reading equal to the class valueof the master. It will be recalled that these same calibration stepswere preformed at the outset of the prediction-gaging step and may berepeated here only to make certain that the settings were not disturbedin the interval between prediction and classification.

At this point, the master 110 is removed and the machined productionvane 10 is replaced in the fixture. The vane is then rocked forwardlythrough the T- gage null position to the forward reset position in thesame manner as during prediction gaging. Arrival of the vane at thereset position triggers the control circuit 330 to illuminate the starttest lamp 346 and reset the digital logic system in the control circuit,as before. The vane is then rocked rearwardly back through the T-gagenull position, again in the same manner as during prediction gaging. inthe present classification-gaging step, however,

rearward rocking of the vane is continued through the T-gage nullposition to a rear limiting or data stored position, after which thevane is again rocked forwardly through a test complete position whereinthe machined class surface of the vane parallels the fixture baseplate1'12.

In the later description of the control circuit 330, it will be seenthat rearward rotation of the vane 10 through the T-gage null positionin the classification-gaging mode of the instrument operates the relay325 for the U-gage sample/hold circuit 326 from its illustrated normalposition to cause the latter circuit to store the input voltage to thecircuit at the instant of passage of the vane through the T-gage nullposition. As noted earlier, this input voltage and hence stored voltagerepresents the product of the AU dimension of the vane (measured at theT-gage null position) and the class formula constant represented by thesetting of the corresponding voltage divider 3141. it will also appearfrom the description of the con trol circuit 330 that the output of theT-gage transducer 185 in the rear limiting or data stored position ofthe vane 10 triggers the control circuit to illuminate a data storedlamp 356 to indicate that the rear position has been reached and the AUsignal has been stored. The latter T-gage transducer output also resetsthe digital logic system of the control circuit to monitor the output ofthe W-gage transducer 246, or more accurately, the output of the W-gagebuffer amplifier 318.

At this point, it is significant to recall that the W-gage transducer2A6 was initially nulled with the master fixed in its basic class angleposition in the fixture 102. in this position, the class surface of themaster parallels the fixture baseplate 112. Accordingly, a null outputfrom the Wgage transducer when the machined production vane 10 ismounted in the fixture indicates that the class surface of the vaneparallels the fixture baseplate.

in the present classification-gaging mode of the instrument, the vane 10is rocked forwardly from its rear data stored position to the positionwherein the W-gage transducer 246 produces a null output indicating thatthe vane class surface then parallels the fixture baseplatie 112. Fromthe later description of the control circuit 330, it will be seen thatthis null signal from the W-gage transducer triggers the control circuitto operate the summing amplifier relay 323 from its normal position,feed a strobe signal to the digital voltmeter 328, and illuminate thetest complete lamp 354. Operation of the relay 323 from its normalposition causes the sample/hold circuit 324, 348 to store the inputvoltage to the circuit at the instant of passage of the vane 10 throughthe null position of the W-gage transducer 246. The strobe signal to thevoltmeter activates the latter to display a reading related to thisstored voltage, which reading is the true class value of the machinedvane 10.

In connection with the latter operation of the instrument, it is evidentthat the above input voltage which is stored in the sample/hold circuit324, 348 in the classification gaging mode of the instrument is the sumof the output voltage from the class value resistor 338, the outputvoltage from the U-gage buffer amplifier 318 in the T-gage null positionof the vane, and the output voltages from the R, S, and T-gage bufferamplifiers in the W-gage null position of the vane. The latter outputvoltage from the U-gage buffer amplifier represents the product of theAU dimension of the vane (measured at the T- gage null position) and theclass formula constant represented by the setting of the correspondingvoltage divider 314. The latter output voltage from each R, S, andT-gage buffer amplifier represents the product of the corresponding vanedelta dimension AR, AS, or AT, as the case :may be (measured at theW-gage null position) and the class formula constant represented by thesetting of the respective voltage divider.

As will appear from the ensuing description, the above AR, AS, AT, andAU dimensions constitute the variables of the classification formulawhich is used to compute the true class value of the machined productionvane in the classificationgaging mode of the instrument. The voltage sumwhich is stored in the sample/hold circuit 324, 348 in the presentclassification-gaging mode represents this true class value, and thedigital voltmeter 328 displays the stored voltage as the true classvalue or numerical class designation of the vane.

At this point, it is significant to recall that the present gaginginstrument is designed to carry out a turbine vane prediction andclassification-gaging procedure involving the use of class formulas thatexpress a figure of merit of a production vane in terms of its AR, AS,and AU dimensions (measured at the T- gage null position) and the trueclass value of the production vane in terms of its AU dimension(measured at the T-gage null position) and its AR, AS, and AU dimensions(measured at the W-gage null position). Before explaining these formulasfurther, it is helpful to recall the earlier discussion relating toturbine classes. As noted in that discussion, a set of turbine vanes ofany given design are adapted for assembly into an annular configurationwith the class surfaces of the vanes in seating contact with a mountingor bolting surface to form an annular nozzle ring of given diameter,i.e. inside and outside diameter. Each pair of adjacent vanes defines anintervening throat. The total nozzle ring flow area equals the sum ofthe several vane throat areas. Viewed in another way, the nozzle ring asa whole presents a given annular area determined by the inner and outerdiameters of the ring. This annular area is divided into incrementalsectors equal in number to the vanes and each occupied by a vane and itsrespective throat. The area of each sector equals the annular area ofthe nozzle ring divided by the number of vanes. In the followingdiscussion, the equal areas of these sectors are referred to as sectorareas. The fiow area of a vane obviously equals this sector area minusthe blocked area of the vane.

As noted in the earlier discussion, turbine vanes may be installed in anozzle ring in any one of a range of angular positions, by machining theclass surfaces of the vanes to the appropriate angles, in order to varythe vane throat areas and hence the total nozzle ring fiow area. In thisregard, it is apparent that changing the angle of a vane changes itsblocked area and thereby its flow area which equals the differencebetween sector area and blocked area. The difi'erent throat areas whichare provided by these different angular positions are referred to asclasses. Each vane is characterized and designated by its respectiveclass value.

A full range of classes for a particular vane design may include anynumber of classes which are denoted by the numbers l, 2, 3,-N.Typically, the number of classes for a given turbine vane design is inthe range from 15 to 30. In some cases, the classes are divided intohalf classes. The delta angle and delta throat angle between successiveclasses is substantially constant over the entire class range.

It is evident from the foregoing discussion that the numerical classvalue of a turbine vane is proportional to its flow area and the flowarea, in turn, is proportional to the class value. From this it will beunderstood that the difference in flow area of the master 110 andproduction vane is proportional to the difference in their numericalclass values.

Returning now to the matter of the class formulas, i.e. figure of merit"or prediction formula, and true class value" or classification formula,which are used in the present gaging instrument, these formulas arebased on known basic class formulas which express the flow areas A; ofturbine vanes in terms of their R, S, U, and T dimensions. While thesebasic class formulas vary from one vane design to another, they are ofthe general form:

l A =K,K R-K SK,T+K -,UK where K, K are constants determined by eachvane design and the R, S, T, and U dimensions are measured at the classangle of the vane.

The first constant term K, of the above basic class formula actuallyrepresents the sector area allotted to the vane and remaining termsrepresent the blocked area of the vane. As noted earlier, the differencebetween the sector area of a vane and its blocked area equals the flowarea of the vane.

The prediction and classification formulas which the computer 104 usesto compute the figure of merit of the production vane 10 in theprediction-gaging mode of the present instrument and the true classvalue of the vane in the classification-gaging mode are derived from thebasic formula for the particular vane being gaged. The manner in whichthese prediction and classification formulas are derived is notessential to an understanding of the invention. Suffice it to say thatthe prediction formula is of the general form:

(2) AN=K ARK AS+K AU where AN is the difference in class values of themaster and production vane, i.e. the figure of merit of the vane; K Kand K are constants determined by the particular vane design beinggaged; and AR, AS, and AU are the differences in the R, S, and Udimensions of the master and vane as gaged in the present instrumentduring the prediction gaging mode with the tip chord section C of thevane oriented at the same angle relative to the baseplate 1 12 as thetip chord section of the master when the latter occupies its basic classangle position in the fixture. In other words, AR,AS, and AU are the AR,AS, and AU dimensions which are gaged in the prediction-gaging mode ofthe present instrument when the vane rocks through the null position ofthe T-gage transducer 185.

The classification formula which is used in the present instrument is ofthe general form: a

where N is the true class value of the vane; K is the basic class valueof the master; K K and Ky are the same constants as in the predictionformula; K is another constant determined by the vane design beinggaged; AU is the difierence in the airfoil length dimensions U of themaster and vane as gaged in the present instrument during theclassification gaging mode when the vane rocks through the null positionof the T-gage transducer 185; and AR, AS, and AT are the differences inthe R-, S-, and T-dimensions of the master and vane as gaged in thepresent instrument during the classification-gaging mode when the vanerocks through the null position of the W-gage transducer 246.

Referring again to the present gaging instrument, the transducers of thevane gages 152, 154, 155, 156, 158, and 160 are matched to haveapproximately the same voltage output per unit plunger displacement fromthe null position. The voltage divider 314 for gage 152 is set to have aratio equal to the prediction and classification formula constant K Thevoltage dividers for gages 154, 156 are set to have ratios equal to theformula constant K Similarly, the voltage dividers for the gages 155 and158 are set to have ratios equal to the formula constants K and Krespectively. The class value adjustment resistor 336 and the voltagesources 332, 334 provides the master vane class constant K In theoperation of the instrument, the vane gage transducers are initiallynulled, in the manner explained earlier, with the master fixed in itsbasic class angle position in the gaging fixture 102. The selectorswitch 310 is then turned to its gaging position and selector switch toits prediction position and the prediction-trimming resistor 336 isadjusted to obtain a zero reading on the display 354 of the digitalvoltmeter, as explained earlier. While the master is still in thefixture, the R- S-, and U-gage transducers 152, 154, 156, and 158 arecalibrated by effectively introducing known AR, AS, and AU dimensionsinto the instrument, one at a time, and adjusting the gain of thecorresponding amplifier-demodulator 300 to provide on the voltmeter 328the correct figure of merit (AN) readout as obtained by computationusing the appropriate prediction formula (2). This calibration may beaccomplished, for example, by inserting a shim of known thicknessbetween the master 110 and the transducer plunger of each gage andadjusting the gain of the corresponding amplifier-demodulator 300 untilthe correct figure of merit readout is displayed. After this predictioncalibration of the instrument has been accomplished, the latter iscalibrated for its classification mode by turning the selector switch340 to its classify position and then adjusting the class valueadjustment resistor 338 to obtain on the digital voltmeter display 354 areadout equal to the numerical class value (basic class value) of themaster 110. Thisad-

1. A turbine vane-gaging instrument for gaging selected dimensions of aturbine vane comprising: a gaging fixture including means for supportingsaid vane in gaging position, and electrical gaging means for gagingsaid elected dimensions of the vane comprising a number of electricalgages each included a relatively movable element for contacting aselected surface portion of said vane, a relatively stationary element,and means for producing an output voltage representing the relativepositions of said elements; and a computer connected to said gages forcombining the gage voltages according to selected class formulas andproviding readouts representing the combined voltages.
 2. An instrumentaccording to claim 1, wherein: each said gage also includes means foradjusting the position of its stationary element relative to its movableelement along the direction line of relative movement of the respectiveelements.
 3. An instrument according to claim 2 wherein: said computeralso includes means for reading the output voltages of said gagesindividually.
 4. An instrument according to claim 3, wherein: said vaneincludes an airfoil having a longitudinal stacking axis, a trailing edgeand opposite convex and concave surfaces, and a buttress at one end ofsaid airfoil having a class surface presented laterally of said airfoilaxis and confronting shoulder surfaces presented longitudinally of saidairfoil; said selected vane dimensions are R-, S-, U-, and T-dimensions,where said R-, S-, and T-dimensions are effective thickness dimensionsof the airfoil chord sections at selected root and center and tip chordstations of said airfoil each measured between and normal to a planetangent to a selected point on the convex airfoil surface and a planeparallel to said tangent plane and tangent to the concave side of saidtrailing edge at the respective chord station, and said U-dimension isthe distance selected points of said buttress shoulder surfaces; andsaid gages include an R-gage for gaging said R-dimensions S1 and S2gages for gaging said S-dimensions, a T-gage for gaging saidT-dimension, and a U-gage for gaging said U-dimension.
 5. An instrumentaccording to claim 4, wherein: said computer includes the means forderiving a voltage equal to the product of each gage output voltage, andmeans for selectively summing the voltages derived from said gages andproviding a readout representing the voltage sum.
 6. A turbinevane-gaging instrument for gaging selected dimensions of a turbine vane,said vane including an airfoil having a longitudinal stacking axis, atrailing edge and opposite convex and concave surfaces, and a buttressat one end of said airfoil having a class surface presented laterally ofsaid airfoil axis and confronting shoulder surfaces presentedlongitudinally of said airfoil, and said selected vane dimensions beingR-, S-, U-, and T-dimensions, where said R-, S-, and T-dimensions areeffective thickness dimensions of the airfoil chord sections at selectedroot and center and tip chord stations of said airfoil each measuredbetween and normal to a plane tangent to a selected point on the convexairfoil surface and a plane parallel to said tangent plane and tangentto the concave side of said trailing edge at the respective chordstation, and said U-dimension is the distance between selected points ofsaid buttress shoulder surfaces, said instrument comprising: a gagingfixture including means for supporting said vane in gaging position, andelectrical gaging means for gaging said selected dimensions of the vanecomprising an R-gate for gaging said R-dimension, S1 and S2 gages forgaging said S-dimensions, a T-gage for gaging said T-dimension, and aU-gage for gaging said U-dimension; each gage including a relativelymovable element for contacting a selected surface portion of said vane,a relatively stationary element, means for producing an output voltagerepresenting the relative positions of said elements and means foradjusting the position of said stationary element relative to saidmovable element along the direction line of relative movement of therespective elements; and a computer connected to said gages and having aprediction-gaging mode and a classification-gaging mode, said computercomprising means for reading out the gage output voltages individually,means for producing a selected constant voltage, and means for combiningin said prediction gaging mode the voltages derived from said R, S1, S2,and U-gages according to a selected prediction formula and combining insaid classification-gaging mode said constant voltage and the voltagesderived from all said gages according to a selected classificationformula.
 7. An instrument according to claim 6, wherein: said vanesupporting means comprise a pair of root and tip traps located inparallel trap planes for pivotally supporting said vane at its root andtip chord stations on a pivot axis coinciding approximately with saidtrailing edge; said gages comprise linear transducers each having aplunger with an axis normal to a selected plane parallel to said pivotaxis; said R-gage plunger has its axis laterally spaced a predetermineddistance from said pivot axis and mounts within the plane of said roottRap a vane-engaging wheel of predetermined radius; said S1 gage plungerhas its axis laterally spaced a predetermined distance from said pivotaxis and mounts within an intermediate plane between and parallel tosaid trap planes a vane-engaging wheel of predetermined radius; said S2gage plunger has its axis intersecting said pivot axis and located insaid intermediate plane; said T-gage plunger has its axis laterallyspaced a predetermined distance from said pivot axis and mounts withinthe plane of said tip trap a vane-engaging wheel of predeterminedradius; said U-gage plunger has its axis normal to said trap planes andincludes gage pins on a common axis parallel to the latter plunger axisfor engaging said buttress shoulder surface, one gage pin being fixedrelative to said fixture, and means operatively connecting the othergage pin to said U-gage plunger for movement with the latter plungeralong said common axis; said vane has a prediction gaging positionwherein said tip chord section is oriented at a predetermined anglerelative to a reference plane, a first classification-gaging positioncoinciding with said prediction position, and a secondclassification-gaging position wherein said class surface parallels saidreference plane; and said R, S1, S2, and U-dimensions are gaged in saidpredication mode with said vane in said prediction position, saidU-dimension is gaged in said classification mode with said vane in saidfirst classification position, and said R-, S-, and T-dimensions aregaged in said latter mode with said vane in said second classificationposition.
 8. A turbine vane-gaging instrument for gaging correspondingselected dimensions of a master vane and a production vane comprising: agaging fixture including means for supporting each vane in gagingposition, and electrical gaging means for gaging said selecteddimensions of each vane and producing output voltages representing thedifference in the corresponding dimensions of said master vane andproduction vane; and a computer connected to said gaging means forcombining said voltages according to selected class formulas andproviding readouts representing the combined voltages.
 9. An instrumentaccording to claim 8, wherein: said electrical gaging means comprise anumber of electrical gages each including a relatively movable elementfor contacting a selected surface portion of said vane, a relativelystationary element, and means for producing an output voltagerepresenting the relative positions of said elements.
 10. An instrumentaccording to claim 9, wherein: each said gage also includes means foradjusting the position of its stationary element relative to its movableelement along the directional line of relative movement of therespective elements.
 11. An instrument according to claim 10, wherein:said computer also includes means for reading the output voltages ofsaid gages individually.
 12. An instrument according to claim 11,wherein: each said vane includes an airfoil having a longitudinalstacking axis, a trailing edge and opposite convex and concave surfaces,and a buttress at one end of said airfoil having a class surfacepresented laterally of said airfoil axis and confronting shouldersurfaces presented longitudinally of said airfoil; said selected vanedimensions are R-, S-, T-, and U-dimensions, wherein said R-, S-, andT-dimensions are effective thickness dimensions of the airfoil chordsections at selected root, center, and tip chord stations of saidairfoil each measured between and normal to a plane tangent to aselected point on the convex airfoil surface and a plane parallel tosaid tangent plane and tangent to the concave side of said trailing edgeat the respective chord station, and said U-dimension is the distanceselected points of said buttress shoulder surfaces: said gages includean R-gage for gaging said R-dimensioN, S1 and S2 gages for gaging saidS-dimension, a T-gage for gaging said T-dimension and a U-gage forgaging said U-dimension.
 13. An instrument according to claim 12,wherein: said computer includes the means for deriving a voltage equalto the product of each gage output voltage, a selected constant, andmeans for selectively summing the voltages derived from said R, S1, S2,T, and U-gages and providing a readout representing the voltage sum. 14.A turbine vane gaging instrument for gaging selected dimensions of amaster vane and a production vane, each vane including an airfoil havinga longitudinal stacking axis, a trailing edge and opposite convex andconcave surfaces, and a buttress at one end of said airfoil having aclass surface presented laterally of said airfoil axis and confrontingshoulder surfaces presented longitudinally of said airfoil, and saidselected vane dimensions being R-, S-, U-, and T-dimensions, where saidR-, S-, and T-dimensions are effective thickness dimensions of theairfoil chord sections at selected root and center and tip chordstations of said airfoil each measured between and normal to a planetangent to a selected point on the convex airfoil surface and a planeparallel to said tangent plane and tangent to the concave side of saidtrailing edge at the respective chord station, and said U-dimension isthe distance between selected points of said buttress shoulder surfaces,said instrument comprising: a gaging fixture including means forsupporting each vane in gaging position, and electrical gaging means forgaging said selected dimensions of the respective vane comprising anR-gage for gaging said R-dimension, S1 and S2 gages for gaging saidS-dimensions, a T-gage for gaging said T-dimension, and a U-gage forgaging said U-dimension; each gage including a relatively movableelement for contacting a selected surface portion of the respectivevane, a relatively stationary element, means for producing an outputvoltage representing the relative positions of said elements, and meansfor adjusting the position of said stationary element relative to saidmovable element along the direction line of relative movement of therespective elements whereby said gages may be set with the master vanein the fixture to produce output voltages with the production vane inthe fixture representing the difference in the corresponding dimensionsof the master and production vanes; and a computer connected to saidgages and having a prediction-gaging made and a classification-gagingmode, said computer comprising means for reading out said gage outputvoltages individually, means for producing a selected constant voltage,and means for combining in said prediction-gaging mode said outputvoltages from said R, S1, S2, and U-gages according to a selectedprediction formula and combining in said classification-gaging mode saidconstant voltage and said output voltages from all said gages accordingto a selected classification formula.
 15. An instrument according toclaim 14, wherein: said vane-supporting means comprise a pair of rootand tip traps located in parallel trap planes for pivotally supportingeach vane at its root and tip chord stations on a pivot axis coincidingapproximately with said trailing edge; said gages comprise lineartransducers each having a plunger with an axis normal to a selectedplane parallel to said picot axis; said R-gage plunger has its axislaterally spaced a predetermined distance from said pivot axis andmounts within the plane of said root trap a vane-engaging wheel ofpredetermined radius; said S1 gage plunger has its axis laterally spaceda predetermined distance from said pivot axis and mounts within anintermediate plane between and parallel to said trap planes avane-engaging wheel of predetermined radius; said S2 gage plunger hasits axis interseCting said pivot axis and located in said intermediateplane; said T-gage plunger has its axis laterally spaced a predetermineddistance from said pivot axis and mounts within the plane of said tiptrap a vane-engaging wheel of predetermined radius; said U-gage plungerhas its axis normal to said trap planes and includes gage pins on acommon axis parallel to the latter plunger axis for engaging saidbuttress shoulder surface, one gage pin being fixed relative to saidfixture, and means operatively connecting with other page pin to saidU-gage plunger for movement with the latter plunger along said commonaxis; said vane has a prediction-gaging position wherein said tip chordsection is oriented at a predetermined angle relative to a referenceplane, a first classification-gaging position coinciding with saidprediction position, and a second classification-gaging position whereinsaid class surface parallels said reference plane; and said R, S1, S2and U-dimensions are gaged in said prediction mode with said vane insaid prediction position, said U-dimension is gaged in saidclassification mode with said vane in said first classificationposition, and said R-, S-, and T-dimensions are gaged in said lattermode with said vane in said second classification position.
 16. A gagingfixture for a turbine vane-gaging instrument comprising: means forsupporting said vane in gaging position; and electrical gaging means forgaging selected dimensions of said vane including a number of separateelectrical gages, each having a relatively movable element forcontacting a selected surface portion of said vane, a relativelystationary element, and means for producing an output voltagerepresenting the relative positions of said elements.
 17. A fixtureaccording to claim 16, wherein: each said gage also includes means foradjusting the position of its stationary element relative to its movableelement along the direction line of relative movement of the respectiveelements.
 18. A fixture according to claim 17, wherein: said vaneincludes an airfoil having a longitudinal stacking axis, a trailing edgeand opposite convex and concave surfaces, and a buttress at one end ofsaid airfoil having a class surface presented laterally of said airfoiland confronting shoulder surfaces presented longitudinally of saidairfoil; said selected vane dimensions are R-, S-, T-, and U-dimensions,where said R-, S-, and T-dimensions are effective thickness dimensionsof the airfoil chord sections at selected root, center, and tip chordstations of said airfoil each measured between and normal to a planetangent to a selected point on the convex airfoil surface and a planeparallel to said tangent plane and tangent to the concave side of saidtrailing edge at the respective chord station, and said U-dimension isthe distance selected points of said buttress shoulder surfaces; andsaid gages include an R-gage for gaging said R-dimension, S1 and S2gages for gaging said S-dimension, a T-gage for gaging said T-dimension,and a U-gage for gaging said U-dimension.
 19. A gaging fixture forgaging selected dimensions of a master vane and a production vanecomprising: means for supporting said vanes in gaging position; andelectrical gaging means for gaging said selected dimensions of saidvanes and producing output voltages proportional to the difference inthe respective dimensions.
 20. A turbine vane gaging method whichcomprises the steps of: gaging selected corresponding dimensions of amaster vane and a production vane and generating voltages proportionalto the differences in the corresponding gaged dimensions of the vanes;and summing said voltages in accordance with a selected class formulaand producing a readout representing the summed voltages.
 21. The gagingmethod of claim 20, wherein: each vane has an airfoil and a classsurfacE; said selected dimensions are selected dimensions of said vaneairfoil; said class formula is a prediction formula expressing thedifference in the class values of said vanes in terms of the differenceson said selected dimensions; and said readout is a figure of meritrepresenting said difference in class values.
 22. A turbine vane-gagingmethod involving a master vane and a production vane each having anairfoil and a class surface, comprising: gaging selected correspondingdimensions of the master vane and production vane airfoils andgenerating voltages proportional to the differences in the correspondinggaged dimensions of the vanes; summing said voltages in accordance witha prediction formula expressing the difference in the class values ofsaid vanes in terms of the differences on said selected dimensions andproduction a readout representing a figure of merit which is related tosaid difference in class values and may be converted to a predictedangle at which said production vane class surface must be machined toprovide said production vane with a selected class value; and gagingsaid selected airfoil dimensions and corresponding selected classsurface dimensions of said vanes after machining of said production vaneclass surface to said predicted angle, generating output voltagesproportional to the differences in the corresponding gaged dimensions,summing the latter voltages in accordance with a selected classificationformula expressing the true class value of said production vane in termsof the latter dimensional differences, and producing a readoutrepresenting said true class value.